Updating Screen Events - Can't play single player worlds after redstone update

Crashes with Survival or Creative games in single player mode whenever I tell the world to open. I have been able to access the multiplayer game that I have a server for on my system and last night accessed a friend's server.

Minecraft has crashed!      
      ----------------------      

Minecraft has stopped running because it encountered a problem; Updating screen events

A full error report has been saved to C:\Users\Elizabeth\AppData\Roaming\.minecraft\crash-reports\crash-2013-03-16_09.37.21-client.txt - Please include a copy of that file (Not this screen!) if you report this crash to anyone; without it, they will not be able to help fix the crash :(



--- BEGIN ERROR REPORT 71a5d7c3 --------
Full report at:
C:\Users\Elizabeth\AppData\Roaming\.minecraft\crash-reports\crash-2013-03-16_09.37.21-client.txt
Please show that file to Mojang, NOT just this screen!

Generated 3/16/13 9:37 AM

-- Head --
Stacktrace:
	at ajn.h(SourceFile:45)
	at ajn.<init>(SourceFile:31)
	at ajj.<init>(SourceFile:16)
	at ajk.a(SourceFile:83)
	at net.minecraft.client.Minecraft.a(SourceFile:1361)
	at axo.e(SourceFile:166)
	at axo.a(SourceFile:131)
	at axl.a(SourceFile:72)
	at axl.d(SourceFile:127)
	at axl.m(SourceFile:111)

-- Affected screen --
Details:
	Screen name: bjz
Stacktrace:
	at net.minecraft.client.Minecraft.l(SourceFile:1076)
	at net.minecraft.client.Minecraft.K(SourceFile:572)
	at net.minecraft.client.Minecraft.run(SourceFile:524)
	at java.lang.Thread.run(Unknown Source)

-- System Details --
Details:
	Minecraft Version: 1.5
	Operating System: Windows 7 (x86) version 6.1
	Java Version: 1.7.0_09, Oracle Corporation
	Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Oracle Corporation
	Memory: 469264624 bytes (447 MB) / 519110656 bytes (495 MB) up to 1037959168 bytes (989 MB)
	JVM Flags: 2 total; -Xms512m -Xmx1024m
	AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
	Suspicious classes: No suspicious classes found.
	IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
	LWJGL: 2.4.2
	OpenGL: ATI Radeon HD 5800 Series GL version 4.2.12002 Compatibility Profile Context 9.12.0.0, ATI Technologies Inc.
	Is Modded: Probably not. Jar signature remains and client brand is untouched.
	Type: Client (map_client.txt)
	Texture Pack: Default
	Profiler Position: N/A (disabled)
	Vec3 Pool Size: ~~ERROR~~ NullPointerException: null

java.lang.RuntimeException: Failed to check session lock, aborting
	at ajn.h(SourceFile:45)
	at ajn.<init>(SourceFile:31)
	at ajj.<init>(SourceFile:16)
	at ajk.a(SourceFile:83)
	at net.minecraft.client.Minecraft.a(SourceFile:1361)
	at axo.e(SourceFile:166)
	at axo.a(SourceFile:131)
	at axl.a(SourceFile:72)
	at axl.d(SourceFile:127)
	at axl.m(SourceFile:111)
	at net.minecraft.client.Minecraft.l(SourceFile:1076)
	at net.minecraft.client.Minecraft.K(SourceFile:572)
	at net.minecraft.client.Minecraft.run(SourceFile:524)
	at java.lang.Thread.run(Unknown Source)
--- END ERROR REPORT 1fc69d68 ----------